The present invention relates to a compact zoom lens, and more particularly relates to a compact zoom lens suitably used in a lens shutter camera.
Recently, in the field of lens shutter cameras, cameras with thin bodies are widely used in the field of single focal length cameras. Even in the field of zoom lens cameras, there is a great demand for thin type cameras. Therefore, a compact zoom lens, the entire length of which is short, is required.
Conventionally, zoom lenses for use in lens shutter cameras, the ratio of variable magnification of which is 1.5 to 2.5, are generally provided with a zoom lens system comprising a first lens group having positive refractive power, and a second lens group having negative refractive power, wherein the first and second lens groups are successively arranged from the object side. For example, the aforementioned zoom lens system is disclosed in Japanese Patent Application Open to Public Inspection No. 128911/1981. The zoom lens of this system features a telephoto structure, short back focal length, and short total lens length,
Due to the progress of the technology of collapsible zoom lens barrels, it has become more important to reduce the lens cost rather than to reduce the total lens length. If the zoom lens is composed of a smaller number of unit lenses, the total lens length can be reduced, so that the camera body can be made thinner.
A practical zoom lens meeting the aforementioned demands is disclosed in Japanese Patent Application Open to Public Inspection No. 127008/1991. This zoom lens is composed of a first lens group including 1 to 3 unit lenses, and a second lens group including 1 or 2 unit lenses, so that the total number of lenses is not more than 5.
However, in this case, aspherical lenses of a high refractive index are frequently used. For that reason, it is difficult to reduce the cost. In a zoom lens in which the second lens group is a negative lens, the magnification of the second lens group is increased. Therefore, any error caused in the rear portion of the first lens group is extended, and reaches the image surface. Consequently, error sensitivity of this portion is increased. In general, aspherical lenses are made by means of molding, so that the surface accuracy is low compared with spherical glass lenses made by means of grinding. For that reason, the zoom lens disclosed in the aforementioned Patent Application, in which an aspherical surface is formed in the rear portion of the first lens group, is generally difficult to manufacture.
Recently, there is a demand for close-up photography, and most zoom cameras can take close-up photographs, the photographing magnification of which is approximately 1/10.
In general, however, aberration caused in an optical system is varied when a focusing operation is carried out, and the less the number of lenses, the more the aberration becomes. Therefore, the reduction in the number of lenses was incompatible with the performance of close-up photography.